Refractory ceramic materials such as zirconia, alumina, zircon, and the like, have been used in making components of systems for making and handling high-temperature liquid, such a molten metals and glass materials. Desirably, these materials have good mechanical performance and performance stability under the high operating temperature, resistance to oxidation, and resistance to corrosion by the fluid.
For example, zircon has been used in making molten glass handling equipment in manufacturing systems of high-precision glass articles, such as glass sheets for liquid crystal display (LCD) substrates. A leading method for making high-precision glass sheets such as those for LCD substrate is the fusion down-draw process developed by Corning Incorporated, NY, U.S.A. This process involves the use of a bulk refractory forming block called isopipe. The dimensional stability of the isopipe is desirably high so that consistent glass sheets can be produced in an acceptable production cycle of the glass making system. One of the parameters indicating the dimensional stability of the isopipe is the creep rate of the material at the high operating temperature of the forming process under the load of gravity of the molten glass and the block itself Zircon was found to have acceptable creep rate for making relatively short isopipes for making glass sheets having a width of, e.g., about 2000 mm.
However, to make ever larger glass sheets precisely and consistently, materials having even lower creep rate than zircon are desired. One of the materials proposed for making isopipes in place of zircon is xenotime (YPO4) ceramics. Phase-pure YPO4 ceramic has a very high melting point (1990° C.) and a low creep rate at the normal operating temperature of an isopipe.
However, making bulk YPO4 ceramic blocks having acceptable properties is not an easy undertaking. A simple, cost-effective method is highly desired.
The present invention satisfies this and other needs.